Re: Fatigue Of Materials Suresh Pdf
Phyllis Sterlin
Most materials are made of crystals. When materials fail, it is usually the result of defects in the crystal or in the arrangement of multiple crystals in a polycrystalline structure. While much research has been done on metal fatigue at larger scales, new technologies are just now allowing researchers to see how atomic-scale defects nucleate, multiply and interact in materials subjected to monotonic or fatigue loading inside a high-resolution microscope.
Subra Suresh (born 1956) is an Indian-born American bioengineer, materials scientist, and academic. Between 2018 and 2022, he was the fourth President of Singapore's Nanyang Technological University (NTU), where he is also the inaugural Distinguished University Professor. He was the Vannevar Bush Professor of Engineering at the Massachusetts Institute of Technology (MIT), and Dean of the School of Engineering at MIT from 2007 to 2010 before being appointed as Director of the National Science Foundation (NSF) by Barack Obama, where he served from 2010 to 2013. He was the president of Carnegie Mellon University (CMU) from 2013 to 2017.
Suresh was born in 1956[3][4] in Mumbai, India, and graduated from high school in Tamil Nadu at the age of 15. In May 1977, he received his BTech degree from the Indian Institute of Technology Madras in Chennai, graduating with a First Class with Distinction.[5] Suresh received a Master's degree in Mechanical Engineering from Iowa State University in 1979,[6] and a PhD in Mechanical Engineering from Massachusetts Institute of Technology under guidance of Robert O. Ritchie in 1981, specializing in materials science.[5][7]
In his leadership roles at MIT, he helped create new state-of-the-art laboratories, a new undergraduate curriculum in materials science and engineering, the MIT Transportation Initiative, and the Center for Computational Engineering; led MIT's efforts in establishing the Singapore-MIT Alliance for Research and Technology (SMART) Center; and oversaw the recruitment of a record number of women faculty in engineering.[12] As Dean of Engineering, he launched or oversaw a number of MIT's major international programs in Asia, the Middle East, Europe and the Americas.
Suresh's research is focused in three areas: modeling and engineering the mechanical properties of structural and functional materials, the mechanical properties of biological cells and molecules, and the implications of these properties for human disease. His work crosses traditional disciplinary boundaries in engineering, physical sciences, life sciences, and medicine. More than 100 students, postdoctoral fellows, and visiting scholars have been members of his research group, and many now occupy prominent positions in academia, industry, and government worldwide.[citation needed]
Suresh has been elected a fellow or honorary fellow of many materials societies in the United States and India, including the Materials Research Society; ASM International; the Minerals, Metals & Materials Society; the American Society of Mechanical Engineers; the American Ceramic Society; the Indian Institute of Metals; and the Materials Research Society of India.
The resistance of metals and alloys to fatigue crack initiation and propagation is known to be influenced significantly by grain size (e.g., [1]). On the basis of experimental results obtained in microcrystalline (mc) metals with grain sizes typically above 1 μm, it is widely recognized that an increase in grain size generally results in a reduction in the fatigue endurance limit. Here, with all other structural factors approximately held fixed, the endurance limit of initially smooth-surfaced specimens generally scales with the strength of the material, which increases with decreasing grain size. On the other hand, a coarse grain structure can lead to an increase in the fatigue crack growth threshold stress intensity factor range and a decrease in the rate of crack growth owing to such mechanisms as periodic deflections in the path of the fatigue crack at grain boundaries during crystallographic fracture [2], especially in the near-threshold regime of fatigue crack growth (e.g., [3]). The relevance of such broad trends extracted from conventional mc alloys to ultra-fine-crystalline (ufc) metals (grain size typically in the 100 nm to 1 μm range) and nanocrystalline (nc) metals (grain size typically less than 100 nm) is largely unknown at this time. Such lack of understanding is primarily a consequence of the paucity of experimental data on the fatigue response of metals with very fine grains. The fatigue response of metals produced by severe plastic deformation using equal channel angular pressing has been studied [4], [5], [6]. Here, cyclic softening and deterioration in low cycle fatigue response have been found with grain refinement, despite an improvement in the fatigue endurance limit seen in stress-life tests. However, conclusive general trends could not be extracted from such observations in that mc metals with severe initial cold work are also known to exhibit cyclic softening [7]. Comprehensive knowledge of the fatigue properties of nc and ufc metals and alloys is critical to the overall assessment of their usefulness in service applications involving structural components. Inadequate fatigue behavior would likely overshadow several potentially attractive characteristics [8], [9], [10], [11], [12] of fine-grain materials (i.e. enhanced strength, hardness, wear and corrosion resistance).
We have demonstrated that grain refinement in the nc and ufc regimes can have a substantial effect on total life under stress-controlled fatigue and on fatigue crack growth. Specifically, fully dense nc and ufc Ni produced by electrodeposition exhibit substantially higher resistance to stress-controlled fatigue compared to conventional mc Ni. However, fatigue crack growth results obtained in this study for nc and ufc Ni also appear to indicate that grain refinement in the nc regime can have a
Written by a leading researcher in the field, this revised and updated second edition of a highly successful book provides an authoritative, comprehensive and unified treatment of the mechanics and micromechanisms of fatigue in metals, non-metals and composites. The author discusses the principles of cyclic deformation, crack initiation and crack growth by fatigue, covering both microscopic and continuum aspects. The book begins with discussions of cyclic deformation and fatigue crack initiation in monocrystalline and polycrystalline ductile alloys as well as in brittle and semi-/non-crystalline solids. Total life and damage-tolerant approaches are then introduced in metals, non-metals and composites followed by more advanced topics. The book includes an extensive bibliography and a problem set for each chapter, together with worked-out example problems and case studies. This will be an important reference for anyone studying fracture and fatigue in materials science and engineering, mechanical, civil, nuclear and aerospace engineering, and biomechanics.
In this work we consider high-cycle fatigue (HCF) for materials with transversely isotropic properties in the TO formulation. We incorporate a continuous-time HCF model, in which the stresses are decomposed into longitudinal and transverse directions (Holopainen et al. 2016). This HCF model can handle arbitrary load histories, including non-proportional loads, without use of any cycle-counting algorithm.
Examples of TO formulations with fatigue constraints include Holmberg et al. (2014), where the fatigue constraints were implemented as stress constraints, and Jeong et al. (2018), Collet et al. (2017), and Oest and Lund (2017) which use cycle-counting algorithms. Other examples of structural optimization with fatigue constraints are found in Oest et al. (2017), where the fatigue prediction is done for a simplified damage model assuming a periodic load, and in Gerzen et al. (2017), where sizing optimization is done with fatigue constraints at the welded joints using a cycle-counting algorithm (rainflow-counting). However, these models are restricted to proportional loading histories. Reference Zhang et al. (2019) uses classical techniques, including rainflow-counting, mean stress correction and the Palmgren-Miner rule. It treats fatigue life induced by non-proportional loads and is implemented in TO problems. Our recent contribution (Suresh et al. 2020) implements an evolution-based fatigue model in TO problems. The fatigue model is capable of handling arbitrary load histories, including non-proportional loads. However, all of the above-mentioned optimization formulations with fatigue constraints are developed for materials with isotropic properties. Hence, an extension of a fatigue model in TO that can handle anisotropic materials properties is needed for design of AM parts. This motivated us to extend our previous contribution (Suresh et al. 2020) and implement a HCF model for transversely isotropic materials in a TO problem; in this case minimization of mass subject to a HCF constraint.
The continuous-time fatigue model in Ottosen et al. (2008) uses a so-called endurance surface that moves in the stress space. The model is based on ordinary differential equations (ODEs) that govern the time evolution of fatigue damage at each point in the design domain. Damage development only occurs if the stress state lies outside the endurance surface. The flexibility of the model has led to further developments such as Brighenti et al. (2011), where the fatigue is assessed for complex multiaxial load histories, and Ottosen et al. (2018), where the multiaxial fatigue criterion considers stress gradient effects in critical regions like holes and notches. The model has also been extended to account for anisotropic properties in Holopainen et al. (2016), in particular transverse isotropy. Furthermore, the validity range and computational acceleration of the continuous-time HCF model are investigated in Lindström et al. (2020).
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